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<Title>General Curve Fitting</Title>
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<p class="heading0">ChartDirector 7.0 (Java Edition)</p>
<p class="heading1">General Curve Fitting</p>
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<img src="images/curvefitting.png" width='600' height='300'>
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This example demonstrates the LOWESS general purpose curve fitting that is built into ChartDirector.<br><br>
In regression curve fitting, a function type have to be chosen first, and the data are used to compute the best parameters of that function. For example, in polynomial regression, the function type is a polynomial of a given degree, and the data are used to determine the optimal polynomial coefficients.<br><br>
However, in many applications, the function type is not known or not expressible in algebraic form. To handle these cases, ChartDirector supports a general curve fitting algorithm known as LOWESS. For details, please refer to <a href="ArrayMath.lowess.htm">ArrayMath.lowess</a> and <a href="ArrayMath.lowess2.htm">ArrayMath.lowess2</a>.<br><br>
The LOWESS algorithm only adjusts the points to smoothen them. They still need to be joined together. In this example, the adjusted points are joined with a spline layer using <a href="XYChart.addSplineLayer.htm">XYChart.addSplineLayer</a>.
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<p class="heading1a">Source Code Listing</p>
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<b>[JSP Version]</b> jspdemo/curvefitting.jsp
<div class='codeblock'><code class='pre'>&lt;%@page import="ChartDirector.*, java.util.*" %&gt;
&lt;%
// Use random table to generate a random series. The random table is set to 1 col x 51 rows, with 9
// as the seed
RanTable rantable = new RanTable(9, 1, 51);

// Set the 1st column to start from 100, with changes between rows from -5 to +5
rantable.setCol(0, 100, -5, 5);

// Get the 1st column of the random table as the data set
double[] data = rantable.getCol(0);

// Create a XYChart object of size 600 x 300 pixels
XYChart c = new XYChart(600, 300);

// Set the plotarea at (50, 35) and of size 500 x 240 pixels. Enable both the horizontal and
// vertical grids by setting their colors to grey (0xc0c0c0)
c.setPlotArea(50, 35, 500, 240).setGridColor(0xc0c0c0, 0xc0c0c0);

// Add a title to the chart using 18 point Times Bold Itatic font.
c.addTitle("LOWESS Generic Curve Fitting Algorithm", "Times New Roman Bold Italic", 18);

// Set the y axis line width to 3 pixels
c.yAxis().setWidth(3);

// Add a title to the x axis using 12pt Arial Bold Italic font
c.xAxis().setTitle("Server Load (TPS)", "Arial Bold Italic", 12);

// Set the x axis line width to 3 pixels
c.xAxis().setWidth(3);

// Set the x axis scale from 0 - 50, with major tick every 5 units and minor tick every 1 unit
c.xAxis().setLinearScale(0, 50, 5, 1);

// Add a blue layer to the chart
LineLayer layer = c.addLineLayer2();

// Add a red (0x80ff0000) data set to the chart with square symbols
layer.addDataSet(data, 0x80ff0000).setDataSymbol(Chart.SquareSymbol);

// Set the line width to 2 pixels
layer.setLineWidth(2);

// Use lowess for curve fitting, and plot the fitted data using a spline layer with line width set
// to 3 pixels
c.addSplineLayer(new ArrayMath(data).lowess().result(), 0x0000ff).setLineWidth(3);

// Set zero affinity to 0 to make sure the line is displayed in the most detail scale
c.yAxis().setAutoScale(0, 0, 0);

// Output the chart
WebChartViewer viewer = new WebChartViewer(request, "chart1");
viewer.setChart(c, Chart.SVG);

// Include tool tip for the chart
viewer.setImageMap(c.getHTMLImageMap("", "", "title='({x}, {value|2})'"));
%&gt;
&lt;!DOCTYPE html&gt;
&lt;html&gt;
&lt;head&gt;
    &lt;title&gt;General Curve Fitting&lt;/title&gt;
    &lt;!-- Include ChartDirector Javascript Library to support chart interactions --&gt;
    &lt;script type="text/javascript" src="cdjcv.js"&gt;&lt;/script&gt;
&lt;/head&gt;
&lt;body style="margin:5px 0px 0px 5px"&gt;
    &lt;div style="font:bold 18pt verdana;"&gt;
        General Curve Fitting
    &lt;/div&gt;
    &lt;hr style="border:solid 1px #000080; background:#000080" /&gt;
    &lt;div style="font:10pt verdana; margin-bottom:1.5em"&gt;
        &lt;a href="viewsource.jsp?file=&lt;%=request.getServletPath()%&gt;"&gt;View Source Code&lt;/a&gt;
    &lt;/div&gt;
    &lt;!-- ****** Here is the chart image ****** --&gt;
    &lt;%= viewer.renderHTML(response) %&gt;
&lt;/body&gt;
&lt;/html&gt;</code></div>
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